So-called tape streamer drives have been known as drive apparatuses capable of performing recording/reproduction of digital data on magnetic tape. Such tape streamer drives have enormous storage capacities of, for example, from several tens to several hundreds of gigabytes, depending on the tape length of the tape cassette media. Consequently such drives are utilized in a wide range of applications, such as backups of the data recorded on the hard disk or other media of computers, and are also well-suited to storage of image and other data with large data sizes.
In such tape streamer drives, the magnetic tape is made to travel with the tape wound over a rotating drum through a predetermined wrap angle; in addition, the rotating drum is rotated, and by using a magnetic head on the rotating drum to perform recording/reproduction scanning using a helical scan method, high-density recording can be performed. Hence as is well known, data are recorded such that there are successive tracks in the length direction on the magnetic tape, formed so as to have a predetermined inclination angle with respect to the length direction.
In a tape streamer drive as described above, as the format of data recorded on the magnetic tape, for example, a format such as the following has been stipulated.
First, one track is formed as a succession of a predetermined plurality of data units called blocks. A block comprises a header, and user data and parity areas following thereafter.
Further, a fixed-length data unit called a group is stipulated. A group is a data unit formed by an aggregate of data recorded on a predetermined plurality of successive tracks, and is handled as a unit of data recording and reproduction within a tape streamer drive. For example, addition of error correction codes during recording, and error correction processing during reproduction, are performed so as to conclude within a group.
Within a block header, there is provided an area for storing ID information. In this ID information area, different types of information are successively allocated and stored in successive blocks within a track, and this successive allocation is repeated. As one among a plurality of information types used as this ID information, group identification information indicating the group to which the current track belongs is defined. Hence the group identification information within a given track is not stored in all blocks, but is stored in, for example, every block after a predetermined number of blocks, according to the number of information types used as ID information.
Even if group identification information is thus stored in every block after a number of blocks, if the group identification information is read from a certain block, the group of a track which is formed including the block can be identified. That is, the group to which the track belongs can be identified.
Hereupon, in the case of a format as described above, as the ID information inserted into the header for each block, one of the various information types is used. Since for such a format it is not necessary to insert all ID information types into all blocks, header data sizes can be smaller, and therefore there is the advantage that to this extent a greater quantity of user data can be recorded.
However, in a single track, ID information of one certain type is not written to all blocks, so that it must be assumed that all the blocks forming one track have common ID information. As a result, for example, the following problem occurs.
For example, in a tape streamer drive, an operation called read-after-write (RAW) is performed during recording to monitor in block units whether data recording to the magnetic tape has been performed correctly. If recording has not been performed correctly, rewriting is performed. That is, the track containing the data for the block is again recorded in another position.
A problem here is that, as explained above, it must be assumed that all the blocks forming one track have common ID information.
Consequently even if recording was not correctly completed for only one block in a given track, the entire track including the block must be rewritten. In this case, a several number of tracks, from the track containing the block in which the recording error occurred to the track recorded immediately before the rewrite, become dummy tracks. If a plurality of dummy tape portions occur over tracks, the recording capacity of the tape as a whole is reduced. Hence it is desired that read-after-write operations be performed efficiently, such that consumption of the magnetic tape be minimized. Also, when rewriting occurs near a group boundary, after writing tracks in the next group, it may be necessary to rewrite data of tracks in the previous group. In this case, the tracks in the previous group and the tracks in the following group are intermixed in unspecified order.
For example, in the current format, group boundaries can only be identified by reading group identification information recorded intermittently in tracks. However, in a state such as described above in which previous and following groups are intermixed, it is difficult for the tape streamer drive to recognize the track positions which actually delimit groups. The possibility of occurrence of recording and reproduction errors is increased, and to this extent, reliability is degraded.
Thus, with the current ID information format, there are disadvantages such as constraints on rewrite operations, and situations in which the tracks forming a single group are separated and not in succession.